SCIENTIFIC SIDE-LIGHTS 



Imprint 



Incandescence 



or what not, the moment you have reason to 

 think the hour is ripe. The hour may not 

 last long, and while it continues you may 

 safely let all the child's other occupations 

 take a second place. In this way you 

 economize time and deepen skill; for many 

 an infant prodigy, artistic or mathematical, 

 has a flowering epoch of but a few months. 

 JAMES Talks to Teachers, ch. 7, p. 61. 

 (H. H. & Co., 1900.) 



1607. IMPURITIES REJECTED BY 

 GLACIER Popular Belief Founded on Scien- 

 tific Fact. A notion [has been] long enter- 

 tained by the inhabitants of the high Alps, 

 that glaciers possess the power of thrusting 

 out all impurities from them. On the Mer 

 de Glace I have noticed large patches of clay 

 and black mud which evidently came from 

 the body of the glacier, and can therefore 

 understand how natural was this notion of 

 extrusion to people unaccustomed to close 

 observation. But the power of the glacier 

 in this respect is in reality the power of the 

 sun, which fuses the ice above concealed im- 

 purities, and, like the bodies of the guides 

 on the Glacier des Bossons, brings them to 

 the light of day. TYNDALL Forms of Water, 

 p. 144. (A., 1899.) 



1608. IMPURITY OF NATURAL 

 COLORS Green Leaves Seen Red and Blue. 

 The impurity of natural colors is stri- 

 kingly illustrated by an observation recently 

 communicated to me by Mr. Woodbury. On 

 looking through a blue glass at green leaves 

 in sunshine, he saw the superficially re- 

 flected light, blue. The light, on the con- 

 trary, which came from the body of the 

 leaves was crimson. On examination, I 

 found that the glass employed in this ob- 

 servation transmitted both ends of the 

 spectrum, the red as well as the blue, and 

 that it quenched the middle. This furnished 

 an easy explanation of the effect. In the 

 delicate spring foliage the blue of the solar 

 light is for the most part absorbed, and a 

 light, mainly yellowish green, but contain- 

 ing a considerable quantity of red, escapes 

 from the leaf to the eye. On looking at such 

 foliage through the violet glass, the green 

 and the yellow are stopped, and the red 

 alone reaches the eye. Thus regarded, there- 

 fore, the leaves appear like faintly blushing 

 roses, and present a very beautiful appear- 

 ance. With the blue ammonia-sulfate of 

 copper, which transmits no red, this effect 

 is not obtained. As the year advances the 

 crimson gradually hardens to a coppery red ; 

 and in the dark-green leaves of old ivy it is 

 almost absent. Permitting a concentrated 

 beam of white light to fall upon fresh leaves 

 in a dark room, the sudden change from 

 green to red, and from red back to green, 

 when the violet glass is alternately intro- 

 duced across the beam and withdrawn, is 

 very surprising. Looked at through the 

 same glass, the meadows in May appear of 

 a warm purple. TYNDALL Lectures on 

 Light, leet. 1, p. 38. (A., 1898.) 



1609. INATTENTION TO THE UN- 

 IMPORTANT Habitual Sensations IgnoreA 

 Din of Foundry Unnoticed by Its Workers. 

 We do not notice the ticking of the clock, 

 the noise of the city streets, or the roaring 

 of the brook near the house; and even the 

 din of a foundry or factory will not mingle 

 with the thoughts of its workers, if they 

 have been there long enough. When we first 

 put on spectacles, especially if they be of 

 certain curvatures, the ^bright reflections 

 they give of the windows, etc., mixing with 

 the field of view, are very disturbing. In a 

 few days we ignore them altogether. Vari- 

 ous entoptic images, muscce volitantes [flit- 

 ting specks before the eyes], etc., altho con- 

 stantly present, are hardly ever known. 

 The pressure of our clothes and shoes, the 

 beating of our hearts and arteries, our 

 breathing, certain stedfast bodily pains, ha- 

 bitual odors, tastes in the mouth, etc., are 

 examples from other senses of the same 

 lapse into unconsciousness of any too un- 

 changing content a lapse which Hobbes has 

 expressed in the well-known phrase, " Sem- 

 per idem sentire ac non sentire ad idem 

 revert unt " [To feel always and not to feel 

 at all come to the same thing]. JAMES 

 Psychology, vol. i, ch. 11, p. 455. (H. H. & 

 Co., 1899.) 



1610. INCANDESCENCE, COLORS 

 OF, NO PICTURE CAN REPRESENT 



Splendor of Sun's Corona Defies Artist's 

 Skill. Pictures are sometimes drawn which 

 attempt to show the color of these [solar] 

 flames. Some of these have been made at 

 the Observatory of Harvard College, United 

 States, where these phenomena are observed 

 with the greatest care. On one of these 

 plates two magnificent prominences of more 

 than 60,000 miles in height are shown, the 

 first observed on April 29,1872, at 10 o'clock 

 in the morning (25 minutes later it had 

 so much changed that it was not to be rec- 

 ognized) ; the second, on April 15 of the 

 same year, at the same hour. We may thus 

 gain a better impression of them than by 

 black figures. But there is something which 

 a picture can never reproduce the vivacity 

 of the tints which these enormous masses 

 present, and the rapidity of the motions 

 with which they are animated. The best 

 drawings will always be bodies without life, 

 veritable corpses, if we compare them with 

 the grand phenomena of Nature. These in- 

 candescent masses are animated with an in- 

 ternal activity, from which life seems to 

 breathe. They shine with a vivid light, and 

 the colors which adorn them form a specific 

 character, by which we can recognize, thanks 

 to spectrum analysis, the chemical nature of 

 the substances which compose them. Could 

 the most perfect drawings depict this solar 

 life? FLAMMARION Popular Astronomy, bk. 

 iii, ch. 4, p. 275. (A.) 



1611. INCANDESCENCE, PHENOM- 

 ENA OF Black Bodies Emit Most Intense 

 Light. We have employed as our source of 



